It is possible to disrupt a gene(s) on the genome or replace it with a transfected DNA fragment by utilizing a cell's ability for homologous recombination (Non-Patent Literatures 1 and 2). This technique is referred to as gene targeting. This technique has not only been a powerful tool for the analyses of the functions of individual genes, but is also anticipated to be used as an ideal gene therapy or breeding method (Non-Patent Literature 3). However, the efficiency of gene targeting in common higher animal or plant cells is extremely low, and thus, it has been desired to develop an improved method that copes with this difficulty. Use of an exon-trapping-type targeting vector having a promoter-free marker gene has been shown to reduce the frequency of occurrence of random insertion, probably leading to enhanced gene targeting efficiency (Non Patent Literatures 4 and 5). Nonetheless, the marker gene may be expressed even by random insertion into a non-target gene. Thus, it has been desired to develop improved methods toward more efficient gene targeting.